Bourdon spiral assembly



Feb. 1, 1966 c. H. PERKINS 3,232,115

BOURDON SPIRAL ASSEMBLY Filed Aug. 6, 1962 INVENT OR CHARLES H. PEQKINS ATTORNEYS U ited States Patfil i F 3,232,116. BOURBON SPIRALASSEMBLY V I Charles H. Perlgins, Knoxville, Tenn, assignor'to Ru enshaw Controls Company, Richmond, Va., a corporation of Deiaware Filed Aug. 6, 1962, Se'r. No. 215,136 4 Claims. "(Cl. 73-418) This invention relates to Bourdon tubes of the type utilized in temperature and pressure instruments, gages, and the like and more particularlyto a Bourdon spiral assembly and to a method of forming a Bourdon; spiral.

In temperature and pressure responsive devices, it is common practice to form a Bourdon spring by flattening a tube, spiralling the flattened tube and filling the tube with an expansible fluid or liquid. One end of the tube communicates with the sensing element and the other sealed end is connected to an indicating mechanism whereby variations sensed by the sensing element causes volumetric variations in the fluid which in turn winds r un- Winds the tube spiral. One of the problems such in- "struments is the short fatigue life of the Bourdon tube because its thin wall construction is subject to stresses caused by the pressure changes in the tube; after a short time these stresses frequently lead toprei'nature failure of the tube or inaccurate responses by the Bourdon spring assembly.

It is, therefore, an object of this invention to eliminate the cause of failures in the thin-walled tubing of a deflecting element.

Another object of this invention is to increase the fatigue life of a thin-walled tube element which deflects in response to pressure variations.

Another object of this invention is to reduce the stress in a Bourdon tube.

It is another object of this invention to reinforce the opposite ends of the hollow tube of a Bourdon spring assembly.

This invention has another object in the method of forming a Bourdon tube assembly.

A further object of this invention resides in the method of forming and welding a Bourdon tube assembly.

In the preferred embodiment of this invention, a round tube is successively passed through rollers to form a flattened ellipse, one end of which is arc welded to a pivot stud and the other end of which is seam Welded to and retained in such shape as to receive capillary tubes; the intermediate portion of the flattened tube is then coiled into a spiral whereby the entire tube is reinforced.

Other objects and advantages of the present invention will become apparent from the following description of the accompanying drawing, wherein:

FIG. 1 is a broken plan view of a cylindrical tube utiiized in making the invention;

FIG. 2 is an end view showing the configuration of the tube after the first step of the method;

FIG. 3 is a broken plan view of the tube in FIG. 1 showing the configuration thereof formed by the method of manufacture;

FIG. 4 is an enlarged end view as viewed from the line 44 of FIG. 3;

FIG. 5 is an enlarged section view taken along the line 55 of FIG. 3;

FIG. 6 is a view similar to FIG. 3 showing another step in the method of manufacture;

FIG. 7 is a side elevation of the tube of FIG. 6 showing the spiral configuration thereof formed by another step in the method of manufacture;

FIG. 8 is an end view as viewed from the line 88 of FIG. 7; and

3,232,116 Patented Feb. 1, I966 FIGQ9is an elevation view of a completed assembly of the invention.

Referring now to FIG. 1 of the drawing, the preferred embodiment of this invention is manufactured from a hollowcylindrical tube 10 which is a round thin-walled tube of suitable material, such as stainless steel, seamless tubing. In the first step of the inventive method, the tube 10 .is flattened along its length by passing the round tube 19 between opposed rollers 12 which successively change the contour from a round to a generally flat oval or elliptical tube 14 (FIG. 2). As is illustrated in FIG. 3, the right hand end portion 16 of the tube 14- retains it s flat oval shape and the remaining portion of the tube is then rolled down further so that such remaining portion is formed into a substantially flat oval tube 18 which is flatter than the shaped end portion 16.

The opposed flattened surfaces on the shaped end portion 16 are seam welded at 20 to connect the central portion B (FIG. 4) and the resulting circular marginal edges define a pair of spaced round bores 22 and 24 for a purpose to be described hereinafter. The left hand end of the flattened tube portion 18 is first provided with a seam weld similar to weld 20 and is then perpendicularly bent to form a mounting flange 26 which constitutes the closed end of the tube. The pivot stud 27 has a threaded extension 28 on one end and a longitudinal slot 29 in an opposite end for snugly receiving the tube flange 26 which is secured to the stud 27 by an inert arc weld 30. The flattened tube portion 18 is then spiralled about the pivot stud 27 as shown in FIG. 7 while the tube portion 16 remains straight. It is to be noted that the seam weld 20 extends only along the straight portion 16.

As is illustrated in FIG. 9, the straight portion 16 is secured to the perpendicular bracket 32 of a mounting plate 34 which is adapted to be mounted in a suitable instrument case (not shown). Since the straight portion 16 includes the spaced bores 22 and 24, the outer walls of the bores 22 and 24 are secured to the bracket 32 by inert arc welding including a pair of upper welding tacks 36 and a pair of lower welding tacks 38 (only one of each pair of welding tacks is shown in FIG. 9). A capillary tube 40 is inserted in the bore 22 as far as possible and is are welded at 42 to the outer edge wall of bore 22. The opposite end of the capillary tube 40 communicates with a condition sensing element 43 fixed to a mounting bracket 44. The bore 24 is a charging port and is provided with a similarly welded filler tube which is not seen in the view of FIG. 9. The filler tube is only a short section that is pinched and sealed after the system is charged and which is not utilized thereafter.

The condition sensing element may be either temperature responsive or pressure responsive so that the assembly may be used as a thermal measuring system or as a pressure measuring system. For example, temperature variations sensed by the sensing element 43 causes the expansion or contraction of the fluid in the system and the resulting pressure variations cause the spiral 18 to wind or unwind; the action of the spiral 18 causes rotation of the center pivot stud 27 which is operatively connected to drive a variable recording, controlling or indicating mechanism.

An increase of internal pressure in the flattened tubing wall causes the outer walls, which are parallel to the major axis of the elliptical tube (FIG. 5), to bulge outwardly whereby the dimension A increases from a minimum at point C towards a maximum dimension at the walls which are parallel to the minor axis of the elliptical tube. Such action normally causes a stress increase along the Walls parallel to such minor axis, however, this stress is reduced to approximatey one-eighth of its normal value because of the seam weld 20. A similar stress reduction applies thus preventing bulging of the tubing flange walls which are parallel to the major axis of such flat oval tubing.

. As the tubing is coiled into the spiral shape 18, the curvature results in a reinforcing action since there exists a two to one ratio of stress in a straight portion of flattened ellipitical tubing and 'a curved portion thereof When both are subjected to the same pressure. Inasmuch as the tubing flange 26 is reinforced by the arc weld 30 and the entire straight portion 16 is rein-forced by the seam weld 20, the entire Bourdon tube is reinforced. Such an arrangement permits the spiral assembly to be operated at pressures above the normal range without loss of fatigue life. It is also evident that the reinforced construction is applicable to tubes having a helix or a C configuration; furthermore, the term Bourdon tube as used herein is intended to include any tube which functions by deflection in response to pressure variations.

Inasmuch as the present invention is subject to many modifications and various changes in structural detail, it

'is intended that all matter contained in the foregoing description of the preferred embodiment and shown on the drawing shall be interpreted as illustrative and not in a limiting sense.

What is claimed is: H 1. A Bourdon tube for instrument gages and the like comprising a tube having a flat oval configuration in crosssection, the flat wall portions of the tube having opposed inner surfaces extending parallel to the major axis of the oval, a seam weld at one end of the tube joining the central portions of the opposed inner surfaces of the flat wall portions to thereby reinforce said one end of the tube, and means sealing the opposite end of the tube.

2. A Bourdon tube according to claim 1 wherein, the said one end of the tube is provided with circular marginal edges disposed on opposite ends of the central portion to thereby define a pair of spaced bores adapted for connection to capillary tube means.

3. A Bourdon 'tube accord ing to claim 1 wherein said means sealing the opposite end of the tube includes a seam weld joining the opposed inner surfaces of the flat wall portions to thereby close the tube.

' 4. A Bourdon tube assembly, comprising a tube having a fiat oval configuration in cross-section, the flat wall portions of the tube being adapted to bulge in response to varying pressures within-the tube, said tube including an arcuate intermediate portion between a straight end portion and a flanged end portion, the flat wall portions of the tube having opposed inner surfaces extending parallel to the major axis of the oval, a seamweld at the straight end portion of the tube joining the opposed inner surfaces of the flat wall portions to thereby prevent bulging of the flat wall portions at said straight end portion, means sealing the flanged end portion of the tube, a pivot stud, said pivot stud having a slot for snugly receiving the flanged end portion of the tube to" thereby prevent bulging of the flat wall portions at said flanged end portion, whereby said tube is reinforced throughout its length.

' References Cited by the Examiner UNITED sTATEs PATENTS 745,636 12/1903 Luscomb 73-418 1,345,630 7/1920 Place 73 41s 1,521,343 12/1924 Townsend 73368 X 1,714,988 5/1929 Schlaich 73-418 1,714,989 5/1929 Schlaich 73-418 X 2,477,242 7/1949 Fahy 29 157 2,478,031 8/1949 Visser 29-157 2,495,314 1/1950 Caldwell 73 41s FOREIGN PATENTS 838,657 -5/1952 Germany.

LOUIS R. PRINCE, Primary Examiner.

JOSEPH P. STRIZAK, RICHARD C. QUEISSER,

Examiners. 

1. A BOURDON TUBE FOR INSTRUMENT GAGES AND THE LIKE COMPRISING A TUBE HAVING A FLAT OVAL CONFIGURATION IN CROSSSECTION, THE FLAT WALL PORTIONS OF THE TUBE HAVING OPPOSED INNER SURFACES EXTENDING PARALLEL TO THE MAJOR AXIS OF THE OVAL, A SEAM WELD AT ONE END OF THE TUBE JOINING THE CENTRAL PORTIONS OF THE OPPOSED INNER SURFACES OF THE FLAT WALL PORTIONS TO THEREBY REINFORCE SAID ONE END OF THE TUBE, AND MEANS SEALING THE OPPOSITE END OF THE TUBE. 